This invention relates to photohardenable compositions. More particularly, this invention relates to liquid compositions which are suitable for use as photoresists.
Various types of plating and etching resists have been known and used for many years for various applications (e.g. in making of printed circuitry, printing plates, etc.). Some types of resists are solvent-based and are hardened or solidified after being coated in the desired pattern by driving off the solvent (e.g. with heat). Some other types of resists are light sensitive and are hardened or solidified by exposure to light after coating, whereupon the resist crosslinks or polymerizes to an insoluble state which is not easily removable with conventional solvents.
Although conventional solvent-based resists provide patterns which can later be removed with solvent after the desired plating or etching has been completed, such resists are undesirable by reason of the fact that in the initial formation of the resist pattern, solvent must be removed. The pollution problems attendant with such procedure (i.e. removal of solvent), and the time required to obtain a hardened pattern, are inherent limitations associated with the use of such solvent-based resins.
In many applications it is extremely desirable (and in some cases it is necessary) to be able to remove the resist pattern rapidly and efficiently from a substrate with conventional organic solvent after the required etching or plating of the substrate has been completed. This is particularly true when the etched substrate is passed through a series of baths in which organic solvent flows continuously from the latter baths toward the first bath. Here it is important that the resist be removed in the first bath.
U.S. Pat. No. 4,134,811 (De Poortere et al.) disclose halogenated photopolymerizable compositions which do not present the problem relating to solvent evaporation. However, these materials, when applied to copper or aluminum substrates, are best removed with alkaline solution and are removed only very slowly with conventional organic solvents (i.e. methylene chloride).
U.S. Pat. No. 4,090,936 (Barton) describes photohardenable, liquid compositions useful as photoresists. While these materials, when cured, retain suitable adhesion to substrates and are rapidly removed when exposed to conventional solvents, the present invention represents an improvement over the high temperature performance of these compositions.